Everyone else has said essentially said everything I wanted to better than I could have, but I want you to know you're not alone! I've been struggling with getting clean for 5 years, and I've been to over seven different treatment centers, not including halfway houses and such. Addiction is rampant in my family, and my parents actually met in Narcotics Anonymous, so they have been understanding of my condition, but they unfortunately can't fix me, and I know it scares them. My mom has been sober for 10 years, and she uses AA. I don't think a 12-step program is your only option, but it has worked for my mom, and when I've actually thrown myself into it, it has worked for me, too. The longest time I've had of continuous sobriety is 8 months.
While I'm not an opiate addict, I have suffered from severe withdrawals from alcohol and benzos, as well as many stimulants. I didn't have any physical withdrawals from stimulants, but mentally, I was so depressed that I was extremely suicidal and even made a genuine attempt. The first month is always the hardest for me personally, but keep in mind that it's temporary. I feel a bit hypocritical giving "advice" because I'm currently not clean and sober, but I can most certainly relate to your situation.
Also, I know being a functioning addict isn't seen as something to be commended, but I have admiration for all that you've achieved! I dropped out of HS, and I only have one semester of college under my belt at 23. My dad has spent an inordinate sum of money on treatment, and I really have nothing to show for myself according to the world's standards. So really, addict or not, be proud of yourself.
Most treatment centers, whether lockdown, transitional, or outpatient, use the 12 step method. Like I said, I don't think it's the only route, but if you do seek treatment, be prepared for that. However, there is a lot of support and accountability offered by these institutions, and even just regular NA and AA. I would also suggest finding a detox center (many of which are affordable, just do some research) to help you get off of them. You may be able to find an outpatient facility that can do this for you so it won't interfere with your responsibilities and obligations. Now I'm no expert here, but the opiate addicts to whom I've spoken say that they wouldn't recommend using methadone to kick it. I've heard Suboxone is much better, especially with medical oversight.
Also, just to reiterate what everyone else has said, DON'T BEAT YOURSELF UP! This
is a disease, and don't let other people tell you otherwise. It is not a reflection of your character. I've done innumerable things of which I am beyond ashamed, and self-reproach is something that comes naturally to me. But it does not serve your best interest to hold that mentality. I would suggest practicing affirmations, and using the law of substitution (replacing each negative thought with a positive one -- not just by negating it, but by saying its opposite. Ex: Instead of saying "I'm not a piece of shit", say "I am a person worthy of happiness" or something to that nature).
Anyway, I hope some of this helps, and although I do not know you, feel free to PM me if you ever need to talk. Just an offer.

I wish you the best!